Our objectives include: (1) the evaluation of the hypothesis that the amino acid sequences of the VH and/or VL domains are encoded in the germ line, (2) the further characterization of the VH- containing fragment V micron with respect to binding activity, (3) the measurement and characterization of the reactivity of monomeric IgM antibody which has been attached to membranes by virtue of a hydrophobic anchor covalently linked to the protein and (4) the detection of conformational changes associated with the binding of a bivalent ligand by IgM antibody. The immunological systems used in this study are equine anti-lactose IgM and murine anti-lactose IgM. Purified preparations of antibody from individual animals are subjected to cleavage with 2-nitro-5-thiocyanobenzoic acid to yield V micron fragments. The populations of V micron fragments are characterized by analytical isoelectric focusing involving, in the case of the murine IgM, prior labeling with 1-125 and radioautography. For the membrane studies monomeric anti-lactose IgM will be conjugated with a fluorescent phospholipid anchor and attached to synthetic vesicles and to lymphocyte membranes. Monovalent and bivalent lactose-containing ligands will be used to measure binding constants and to induce structural changes in the membrane.